/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
 *
 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the public domain, as
 * explained at http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.Deque;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * A {@link Deque} that additionally supports blocking operations that wait for the deque to become non-empty when
 * retrieving an element, and wait for space to become available in the deque when storing an element.
 *
 * <p>
 * {@code BlockingDeque} methods come in four forms, with different ways of handling operations that cannot be satisfied
 * immediately, but may be satisfied at some point in the future: one throws an exception, the second returns a special
 * value (either {@code null} or {@code false}, depending on the operation), the third blocks the current thread
 * indefinitely until the operation can succeed, and the fourth blocks for only a given maximum time limit before giving
 * up. These methods are summarized in the following table:
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1> <caption>Summary of BlockingDeque methods</caption>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 5><b>First Element (Head)</b></td>
 * </tr>
 * <tr>
 * <td></td>
 * <td ALIGN=CENTER><em>Throws exception</em></td>
 * <td ALIGN=CENTER><em>Special value</em></td>
 * <td ALIGN=CENTER><em>Blocks</em></td>
 * <td ALIGN=CENTER><em>Times out</em></td>
 * </tr>
 * <tr>
 * <td><b>Insert</b></td>
 * <td>{@link #addFirst addFirst(e)}</td>
 * <td>{@link #offerFirst(Object) offerFirst(e)}</td>
 * <td>{@link #putFirst putFirst(e)}</td>
 * <td>{@link #offerFirst(Object, long, TimeUnit) offerFirst(e, time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Remove</b></td>
 * <td>{@link #removeFirst removeFirst()}</td>
 * <td>{@link #pollFirst pollFirst()}</td>
 * <td>{@link #takeFirst takeFirst()}</td>
 * <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Examine</b></td>
 * <td>{@link #getFirst getFirst()}</td>
 * <td>{@link #peekFirst peekFirst()}</td>
 * <td><em>not applicable</em></td>
 * <td><em>not applicable</em></td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 5><b>Last Element (Tail)</b></td>
 * </tr>
 * <tr>
 * <td></td>
 * <td ALIGN=CENTER><em>Throws exception</em></td>
 * <td ALIGN=CENTER><em>Special value</em></td>
 * <td ALIGN=CENTER><em>Blocks</em></td>
 * <td ALIGN=CENTER><em>Times out</em></td>
 * </tr>
 * <tr>
 * <td><b>Insert</b></td>
 * <td>{@link #addLast addLast(e)}</td>
 * <td>{@link #offerLast(Object) offerLast(e)}</td>
 * <td>{@link #putLast putLast(e)}</td>
 * <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Remove</b></td>
 * <td>{@link #removeLast() removeLast()}</td>
 * <td>{@link #pollLast() pollLast()}</td>
 * <td>{@link #takeLast takeLast()}</td>
 * <td>{@link #pollLast(long, TimeUnit) pollLast(time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Examine</b></td>
 * <td>{@link #getLast getLast()}</td>
 * <td>{@link #peekLast peekLast()}</td>
 * <td><em>not applicable</em></td>
 * <td><em>not applicable</em></td>
 * </tr>
 * </table>
 *
 * <p>
 * Like any {@link BlockingQueue}, a {@code BlockingDeque} is thread safe, does not permit null elements, and may (or
 * may not) be capacity-constrained.
 *
 * <p>
 * A {@code BlockingDeque} implementation may be used directly as a FIFO {@code BlockingQueue}. The methods inherited
 * from the {@code BlockingQueue} interface are precisely equivalent to {@code BlockingDeque} methods as indicated in
 * the following table:
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1> <caption>Comparison of BlockingQueue and BlockingDeque methods</caption>
 * <tr>
 * <td ALIGN=CENTER><b>{@code BlockingQueue} Method</b></td>
 * <td ALIGN=CENTER><b>Equivalent {@code BlockingDeque} Method</b></td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 2><b>Insert</b></td>
 * </tr>
 * <tr>
 * <td>{@link #add(Object) add(e)}</td>
 * <td>{@link #addLast(Object) addLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link #offer(Object) offer(e)}</td>
 * <td>{@link #offerLast(Object) offerLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link #put(Object) put(e)}</td>
 * <td>{@link #putLast(Object) putLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
 * <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 2><b>Remove</b></td>
 * </tr>
 * <tr>
 * <td>{@link #remove() remove()}</td>
 * <td>{@link #removeFirst() removeFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #poll() poll()}</td>
 * <td>{@link #pollFirst() pollFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #take() take()}</td>
 * <td>{@link #takeFirst() takeFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
 * <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 2><b>Examine</b></td>
 * </tr>
 * <tr>
 * <td>{@link #element() element()}</td>
 * <td>{@link #getFirst() getFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #peek() peek()}</td>
 * <td>{@link #peekFirst() peekFirst()}</td>
 * </tr>
 * </table>
 *
 * <p>
 * Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into
 * a {@code BlockingDeque} <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> actions subsequent
 * to the access or removal of that element from the {@code BlockingDeque} in another thread.
 *
 * <p>
 * This interface is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections
 * Framework</a>.
 *
 * @since 1.6
 * @author Doug Lea
 * @param <E>
 *            the type of elements held in this collection 这个类也是线程通信的工具，线程安全的队列、有界无界队列，在线程池中、rocketMQ、nacos、Netty中均使用到
 *            任意时刻，不管并发有多高，在单JVM中，同一时刻，永远只有一个线程进行入队或者出队操作
 */
public interface BlockingDeque<E> extends BlockingQueue<E>, Deque<E> {
    /*
     * We have "diamond" multiple interface inheritance here, and that
     * introduces ambiguities.  Methods might end up with different
     * specs depending on the branch chosen by javadoc.  Thus a lot of
     * methods specs here are copied from superinterfaces.
     */

    /**
     * Inserts the specified element at the front of this deque if it is possible to do so immediately without violating
     * capacity restrictions, throwing an {@code IllegalStateException} if no space is currently available. When using a
     * capacity-restricted deque, it is generally preferable to use {@link #offerFirst(Object) offerFirst}.
     *
     * @param e
     *            the element to add
     * @throws IllegalStateException
     *             {@inheritDoc}
     * @throws ClassCastException
     *             {@inheritDoc}
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             {@inheritDoc}
     */
    void addFirst(E e);

    /**
     * Inserts the specified element at the end of this deque if it is possible to do so immediately without violating
     * capacity restrictions, throwing an {@code IllegalStateException} if no space is currently available. When using a
     * capacity-restricted deque, it is generally preferable to use {@link #offerLast(Object) offerLast}.
     *
     * @param e
     *            the element to add
     * @throws IllegalStateException
     *             {@inheritDoc}
     * @throws ClassCastException
     *             {@inheritDoc}
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             {@inheritDoc}
     */
    void addLast(E e);

    /**
     * Inserts the specified element at the front of this deque if it is possible to do so immediately without violating
     * capacity restrictions, returning {@code true} upon success and {@code false} if no space is currently available.
     * When using a capacity-restricted deque, this method is generally preferable to the {@link #addFirst(Object)
     * addFirst} method, which can fail to insert an element only by throwing an exception.
     *
     * @param e
     *            the element to add
     * @throws ClassCastException
     *             {@inheritDoc}
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             {@inheritDoc}
     */
    boolean offerFirst(E e);

    /**
     * Inserts the specified element at the end of this deque if it is possible to do so immediately without violating
     * capacity restrictions, returning {@code true} upon success and {@code false} if no space is currently available.
     * When using a capacity-restricted deque, this method is generally preferable to the {@link #addLast(Object)
     * addLast} method, which can fail to insert an element only by throwing an exception.
     *
     * @param e
     *            the element to add
     * @throws ClassCastException
     *             {@inheritDoc}
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             {@inheritDoc}
     */
    boolean offerLast(E e);

    /**
     * Inserts the specified element at the front of this deque, waiting if necessary for space to become available.
     *
     * @param e
     *            the element to add
     * @throws InterruptedException
     *             if interrupted while waiting
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    void putFirst(E e) throws InterruptedException;

    /**
     * Inserts the specified element at the end of this deque, waiting if necessary for space to become available.
     *
     * @param e
     *            the element to add
     * @throws InterruptedException
     *             if interrupted while waiting
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    void putLast(E e) throws InterruptedException;

    /**
     * Inserts the specified element at the front of this deque, waiting up to the specified wait time if necessary for
     * space to become available.
     *
     * @param e
     *            the element to add
     * @param timeout
     *            how long to wait before giving up, in units of {@code unit}
     * @param unit
     *            a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
     * @return {@code true} if successful, or {@code false} if the specified waiting time elapses before space is
     *         available
     * @throws InterruptedException
     *             if interrupted while waiting
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    boolean offerFirst(E e, long timeout, TimeUnit unit) throws InterruptedException;

    /**
     * Inserts the specified element at the end of this deque, waiting up to the specified wait time if necessary for
     * space to become available.
     *
     * @param e
     *            the element to add
     * @param timeout
     *            how long to wait before giving up, in units of {@code unit}
     * @param unit
     *            a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
     * @return {@code true} if successful, or {@code false} if the specified waiting time elapses before space is
     *         available
     * @throws InterruptedException
     *             if interrupted while waiting
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    boolean offerLast(E e, long timeout, TimeUnit unit) throws InterruptedException;

    /**
     * Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.
     *
     * @return the head of this deque
     * @throws InterruptedException
     *             if interrupted while waiting
     */
    E takeFirst() throws InterruptedException;

    /**
     * Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.
     *
     * @return the tail of this deque
     * @throws InterruptedException
     *             if interrupted while waiting
     */
    E takeLast() throws InterruptedException;

    /**
     * Retrieves and removes the first element of this deque, waiting up to the specified wait time if necessary for an
     * element to become available.
     *
     * @param timeout
     *            how long to wait before giving up, in units of {@code unit}
     * @param unit
     *            a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
     * @return the head of this deque, or {@code null} if the specified waiting time elapses before an element is
     *         available
     * @throws InterruptedException
     *             if interrupted while waiting
     */
    E pollFirst(long timeout, TimeUnit unit) throws InterruptedException;

    /**
     * Retrieves and removes the last element of this deque, waiting up to the specified wait time if necessary for an
     * element to become available.
     *
     * @param timeout
     *            how long to wait before giving up, in units of {@code unit}
     * @param unit
     *            a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
     * @return the tail of this deque, or {@code null} if the specified waiting time elapses before an element is
     *         available
     * @throws InterruptedException
     *             if interrupted while waiting
     */
    E pollLast(long timeout, TimeUnit unit) throws InterruptedException;

    /**
     * Removes the first occurrence of the specified element from this deque. If the deque does not contain the element,
     * it is unchanged. More formally, removes the first element {@code e} such that {@code o.equals(e)} (if such an
     * element exists). Returns {@code true} if this deque contained the specified element (or equivalently, if this
     * deque changed as a result of the call).
     *
     * @param o
     *            element to be removed from this deque, if present
     * @return {@code true} if an element was removed as a result of this call
     * @throws ClassCastException
     *             if the class of the specified element is incompatible with this deque
     *             (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException
     *             if the specified element is null (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    boolean removeFirstOccurrence(Object o);

    /**
     * Removes the last occurrence of the specified element from this deque. If the deque does not contain the element,
     * it is unchanged. More formally, removes the last element {@code e} such that {@code o.equals(e)} (if such an
     * element exists). Returns {@code true} if this deque contained the specified element (or equivalently, if this
     * deque changed as a result of the call).
     *
     * @param o
     *            element to be removed from this deque, if present
     * @return {@code true} if an element was removed as a result of this call
     * @throws ClassCastException
     *             if the class of the specified element is incompatible with this deque
     *             (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException
     *             if the specified element is null (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    boolean removeLastOccurrence(Object o);

    // *** BlockingQueue methods ***

    /**
     * Inserts the specified element into the queue represented by this deque (in other words, at the tail of this
     * deque) if it is possible to do so immediately without violating capacity restrictions, returning {@code true}
     * upon success and throwing an {@code IllegalStateException} if no space is currently available. When using a
     * capacity-restricted deque, it is generally preferable to use {@link #offer(Object) offer}.
     *
     * <p>
     * This method is equivalent to {@link #addLast(Object) addLast}.
     *
     * @param e
     *            the element to add
     * @throws IllegalStateException
     *             {@inheritDoc}
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    boolean add(E e);

    /**
     * Inserts the specified element into the queue represented by this deque (in other words, at the tail of this
     * deque) if it is possible to do so immediately without violating capacity restrictions, returning {@code true}
     * upon success and {@code false} if no space is currently available. When using a capacity-restricted deque, this
     * method is generally preferable to the {@link #add} method, which can fail to insert an element only by throwing
     * an exception.
     *
     * <p>
     * This method is equivalent to {@link #offerLast(Object) offerLast}.
     *
     * @param e
     *            the element to add
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    boolean offer(E e);

    /**
     * Inserts the specified element into the queue represented by this deque (in other words, at the tail of this
     * deque), waiting if necessary for space to become available.
     *
     * <p>
     * This method is equivalent to {@link #putLast(Object) putLast}.
     *
     * @param e
     *            the element to add
     * @throws InterruptedException
     *             {@inheritDoc}
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    void put(E e) throws InterruptedException;

    /**
     * Inserts the specified element into the queue represented by this deque (in other words, at the tail of this
     * deque), waiting up to the specified wait time if necessary for space to become available.
     *
     * <p>
     * This method is equivalent to {@link #offerLast(Object,long,TimeUnit) offerLast}.
     *
     * @param e
     *            the element to add
     * @return {@code true} if the element was added to this deque, else {@code false}
     * @throws InterruptedException
     *             {@inheritDoc}
     * @throws ClassCastException
     *             if the class of the specified element prevents it from being added to this deque
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             if some property of the specified element prevents it from being added to this deque
     */
    boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException;

    /**
     * Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this
     * deque). This method differs from {@link #poll poll} only in that it throws an exception if this deque is empty.
     *
     * <p>
     * This method is equivalent to {@link #removeFirst() removeFirst}.
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException
     *             if this deque is empty
     */
    E remove();

    /**
     * Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this
     * deque), or returns {@code null} if this deque is empty.
     *
     * <p>
     * This method is equivalent to {@link #pollFirst()}.
     *
     * @return the head of this deque, or {@code null} if this deque is empty
     */
    E poll();

    /**
     * Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this
     * deque), waiting if necessary until an element becomes available.
     *
     * <p>
     * This method is equivalent to {@link #takeFirst() takeFirst}.
     *
     * @return the head of this deque
     * @throws InterruptedException
     *             if interrupted while waiting
     */
    E take() throws InterruptedException;

    /**
     * Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this
     * deque), waiting up to the specified wait time if necessary for an element to become available.
     *
     * <p>
     * This method is equivalent to {@link #pollFirst(long,TimeUnit) pollFirst}.
     *
     * @return the head of this deque, or {@code null} if the specified waiting time elapses before an element is
     *         available
     * @throws InterruptedException
     *             if interrupted while waiting
     */
    E poll(long timeout, TimeUnit unit) throws InterruptedException;

    /**
     * Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first
     * element of this deque). This method differs from {@link #peek peek} only in that it throws an exception if this
     * deque is empty.
     *
     * <p>
     * This method is equivalent to {@link #getFirst() getFirst}.
     *
     * @return the head of this deque
     * @throws NoSuchElementException
     *             if this deque is empty
     */
    E element();

    /**
     * Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first
     * element of this deque), or returns {@code null} if this deque is empty.
     *
     * <p>
     * This method is equivalent to {@link #peekFirst() peekFirst}.
     *
     * @return the head of this deque, or {@code null} if this deque is empty
     */
    E peek();

    /**
     * Removes the first occurrence of the specified element from this deque. If the deque does not contain the element,
     * it is unchanged. More formally, removes the first element {@code e} such that {@code o.equals(e)} (if such an
     * element exists). Returns {@code true} if this deque contained the specified element (or equivalently, if this
     * deque changed as a result of the call).
     *
     * <p>
     * This method is equivalent to {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
     *
     * @param o
     *            element to be removed from this deque, if present
     * @return {@code true} if this deque changed as a result of the call
     * @throws ClassCastException
     *             if the class of the specified element is incompatible with this deque
     *             (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException
     *             if the specified element is null (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    boolean remove(Object o);

    /**
     * Returns {@code true} if this deque contains the specified element. More formally, returns {@code true} if and
     * only if this deque contains at least one element {@code e} such that {@code o.equals(e)}.
     *
     * @param o
     *            object to be checked for containment in this deque
     * @return {@code true} if this deque contains the specified element
     * @throws ClassCastException
     *             if the class of the specified element is incompatible with this deque
     *             (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException
     *             if the specified element is null (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    public boolean contains(Object o);

    /**
     * Returns the number of elements in this deque.
     *
     * @return the number of elements in this deque
     */
    public int size();

    /**
     * Returns an iterator over the elements in this deque in proper sequence. The elements will be returned in order
     * from first (head) to last (tail).
     *
     * @return an iterator over the elements in this deque in proper sequence
     */
    Iterator<E> iterator();

    // *** Stack methods ***

    /**
     * Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is
     * possible to do so immediately without violating capacity restrictions, throwing an {@code IllegalStateException}
     * if no space is currently available.
     *
     * <p>
     * This method is equivalent to {@link #addFirst(Object) addFirst}.
     *
     * @throws IllegalStateException
     *             {@inheritDoc}
     * @throws ClassCastException
     *             {@inheritDoc}
     * @throws NullPointerException
     *             if the specified element is null
     * @throws IllegalArgumentException
     *             {@inheritDoc}
     */
    void push(E e);
}
